Linux guest and host, guest can't boot with IO-APIC after update to 3.0.12

I've been running a CentOS 5.4 64-bit guest (kernel 2.6.18-164.6.1.el5) under a Fedora 11 64-bit host (kernel 2.6.30.9-96.fc11.x86_64), with VirtualBox 3.0.10 and ACPI, IO-APIC and AMD-V enabled. After the update to 3.0.12, the guest would no longer boot (it got a kernel panic immediately). I disabled IO-APIC in the configuration, and the guest boots again.